The Serial Port: Never Say Die

The classic communications port has a huge installed base and new devices are still using it.

Just because today's consumer-grade computers no longer include the venerable serial port doesn't mean the legacy port is dead.

Quite to the contrary, the serial port is still thriving in industrial controls, medical devices, and automated test systems. In fact, there's a good change you still use the serial port on your test bench when you need a quick connection and measurement. As a result, you'll find RS-232, RS-422, RS-485, and other serial ports on millions of devices in use today.

Sealevel Systems has been designing and manufacturing serial-port interface for many years. With new PCs lacking serial ports, the need to keep systems running on new computers has fueled a need for more serial-port interfaces. Today, the company announced another pair of serial-port interface card for desktop and industrial computers.

The $459 5102e adds one RS-232, RS-422, RS-485, RS-530, RS-530A, or V.35 to any PCIe port. The type of port is software selectable and is available through the card's DB-25 connector. Sealevel has also introduced an RS232-only cards for $449, the 5103e.

I started writing about the demise of the serial port about a decade ago, even as 232 and 485 chipsets continued to grow (albeit at single digit percentages). There's no question that the venerable serial port has been losing market share to more structured, newer standards. But, there is so much growth in the number and types of devices that have embedded processors, that don't need full-fledged networking capability that it's overwhelmed the obsolescence trend.

Particularly in non-consumer market equipment - everything from HVAC to DCNC's to ovens, controllers, relays, RTU's, inverters and more - serial ports (particularly RS-485) continue to be the default port, with things like Ethernet available often at a very hefty upsell cost.

Someday it will be an artifact, but with people connecting more and more "stuff" (whether you call it IoT or M2M...). Much of that stuff is capital equipment that will be in place for 10 years or more, there is a large demand for all kinds of serial converter type products.

These days, our fastest growing items are no longer converting or isolating serial to serial type connections (ie 232 to 485) but they're converting 232 or 485 over to USB, Ethernet or WiFi.

> Now you just plug in the USB cable and (mostly) away you go. That is a very good thing.

Is it? Are you sure? USB has at least 5 types of connector that I know of. And how often do you not have a cable with the one you need handy? At least with serial you could carry around a few 9-25 and M-F adaptors (or plugs with a soldering iron) and you could get yourself out of trouble.

At work I use the Dxx (D-9 or D-25 M or F) to RJ45 adapters. You can configure the pins how you want. I have a couple of "PC-Standard" adapters and then others for the various equipments we use. Plus a 1-metre and a 3-meter Cat-5 cable and that connects me to most of the things we connect to, without carrying a mass of cables around. With those and a breakout box you can't go wrong....

@BobGroh...weell nothing new that I have seen has a serial interface connector any more (I guess that's why no laptops have them). But we still have heaps of Legacy equipment around that needs it, and some of them will be around for a fair while yet. And the RS422/485 incarnations will last even longer - places like B&B Electronics make good business out of connecting Serial legacy equipment over modern comms media. But how long will they be around - another 10 or 20 years I'd guess?

@BobGroh, yeah, the (usually improper) way people interpreted the interface, the handshaking, and the baud rates could be a PITA as you say. But it did not need much knowledge to get round that. A breakout box and a soldering iron could get you out of trouble most of the time. Certainly I never had one beat me. The most memorable one was a shoe leather pattern cutter that a guy had been trying to get working on his PC for a few months. I got it going in about 10 minutes (and got a nice fee for my trouble). And you could make up your own cables, as long (within limits, which were a lot more than USB) or as short as you wished. Yeah, sure, USB pumps a lot more data through, but at low baud rates you can use a bit of wet string and you'll get through, And if that doesn't work, stick a couple of modems in between....

I've used (and still use) serial to communicate with PABXs, 2-way radios and radio modems and other comms equipment - admittedly mostly legacy stuff. My work laptop no longer has a serial port on it and so I have to carry around a USB to serial adapter (and that is a PITA when you discover, out in the field, that you brought your laptop but the USB lead is still in the workshop back home....)

I must admit that for convenience with most connections (from a PC to a printer / camera / phone etc) USB is hard to beat. But I had a lot of fun with RS232 stuff - see my article

No, wait! I take that back (sort of). The old serial RS-232 port was a bit of PITA at times - deciding what control lines were being used, what state they should be in, what the sex of the connectors should be, etc. Argggggh!!!

However, as one commentor said, you could throw together something (software-wise) and bit-bang an interface. And certainly there were several little programs you could use to send and receive the data.

But then again you had to worry about the baud rate (there - I've revealed my age a bit - baud rate, who the heck uses that anymore) and those darned control lines.

And about the ease of bit-banging et al. With today's window based applications, that is sure not as easy as it used to be.

Now you just plug in the USB cable and (mostly) away you go. That is a very good thing.

RS232 running at TTL levels is simply the easiest, most universal and most hassle-free way I know of to connect just about any two programmable devices, from 8-pin MCUs to tablets to PCs to many instruments. And I've always had great luck with inexpensive RS232 USB dongles (at TTL levels, give or take), so it will do for a driver-free USB interface as well. And there's no end of software available for it, from bit-banged ports to full-up terminal programs.